It lists the opcodes for instructions of the form "ADC $ABCD" and "ADC $ABCD, X" as 0x60 and 0x70 respectively, but this is contradicted by two other documents ( http://nesdev.com/opcodes.txt ) and 6502jsm.doc in ( http://nesdev.com/6502jsm.zip ), which state that the opcodes are 0x6d and 0x7d respectively.

Sorry if this was already mentioned. I ran a couple of searches but they didn't turn up anything that looked related on this message board.

That document is also wrong in the way it describes negative branches (it implies that $FF is a branch of -127 when it's really a branch of -1) I recall its opcodes being off in the occasional area as well (like the ones you brought up).

It would be good to get some kind of a note about this matter on NesDev or take the whole document away once and for all. The link Disch gave seems decent, and it's also much more nicer to read HTML-formatted documents than ASCII

Most of that document was copied straight from the oldskool c64 programmer's reference manual...actually it *is* listed correctly in the opcode table and in the ADC opcode list of the actual manual...problem is, whoever copied out of the book most likely made typing errors. I don't exactly see where in the doc it implies that FF is -127.

Having said all of that, I find the instruction source code following the opcode table all but useless. But that's just my opinion.

The pseudo code for each instruction at the bottom is very useful when starting out for a more detailed explaination of how the instructions work. 6502.txt also gets into more detail and explains things a little better than some other docs -- but due to misprints/errors it's not reliable for lookup/reference of the technical details (like opcode numbers, possibly even cycle counts). The link I gave before is consitant and 100% error free -- and could be used as a "last word" on that stuff -- which is why I brought it up.

Heh... that example looks strikingly like signed magnitude representation of signed numbers, which is wrong - the 6502 uses two's complement (where, to get a negative version of a number, you invert all of the bits and then add 1).

_________________Quietust, QMT Productions
P.S. If you don't get this note, let me know and I'll write you another.

Who is online

Users browsing this forum: No registered users and 10 guests

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum